Cochlin-tomoprotein (hereinafter referred to as CTP), which is a 16 kDa isoform of Cochlin present in perilymph, is a promising diagnostic marker for perilymph fistula because it is not found in other body fluids which can be present in the middle ear such as cerebrospinal fluid, blood and saliva (Patent Literature 1, Nonpatent Literatures 1-5). Perilymph fistula is a disease in which inner ear dysfunction is manifested when labyrinthine window separating the inner ear from the middle ear is ruptured, and then perilymph with which the inner ear is filled leaks into the middle ear. Because the symptom may be ameliorated by closing labyrinthine window in the early stage of the onset, early diagnosis is very important.
So far, the research group of the present inventors has produced four rabbit polyclonal antibodies using a synthetic peptide as an immunogen in order to measure CTP in a biological sample (Patent Literature 1). However, all of the antibodies only react with denatured CTP. An antibody reacting with native CTP has not been obtained. In Nonpatent Literatures 1-5, therefore, the above anti-LCCL3 antibody which recognizes denatured CTP (which does not react with native CTP) is used to measure CTP in a biological sample by Western blotting.